The present disclosure relates to optical systems for use in conjunction with flood and area lights for work site illumination and emergency vehicles.
Halogen, metal halide, mercury vapor, sodium vapor, arc lamps and other light sources have been employed in floodlights. Floodlights typically employ a weather-resistant, hermetic housing surrounding the light source. The light source is typically positioned in front of a reflector and behind a lens, each of which are configured to redirect light from the light source into a large area diverging beam of light. Traditional floodlights are typically mounted so that the direction of the light beam can be adjusted with respect to the horizontal, allowing the floodlight to illuminate areas above or below the height of the light. The floodlight support may also permit rotation of the light.
When floodlights are employed in conjunction with emergency response vehicles such as fire trucks, ambulances or rescue vehicles, they may be mounted to a pole which allows the elevation and orientation of the floodlight to vary with respect to the vehicle. Alternatively, floodlights may be mounted to the top front corner of the cab (so called “brow lights”), or the floodlights are mounted in an enclosure secured to a vertical side or rear face of the vehicle body. It is frequently desirable for the floodlight to illuminate an area of the ground surrounding the vehicle. In such cases, floodlights are typically directed downward to produce the desired illumination pattern.
While prior art floodlights have been suitable for their intended purpose, prior art light sources suffer from excessive energy consumption and relatively short life spans. Light emitting diode (LED) light sources are now commercially available with sufficient intensity of white light to make them practical as an alternative light source for flood and area lighting. The semiconductor chip or die of an LED is typically packaged on a heat-conducting base which supports electrical connections to the die and incorporates some form of lens over the die to shape light emission from the LED. Such packages including a base with electrical connections and thermal pathway, die and optic are typically referred to as an LED lamp. Generally speaking, LED lamps emit light to one side of a plane including the light emitting die and are therefore considered “directional” light sources. The light emission pattern of an LED is typically measured and described with respect to an optical axis projecting from the die of the LED and perpendicular to the plane including the die. A hemispherical (lambertian) pattern of light emission can be described as having an angular distribution of two pi steradians.
Although the total optical energy emitted from an LED lamp continues to steadily improve, it is still typically necessary to combine several LED lamps to obtain the optical energy necessary for a given illumination pattern. Optical systems are employed to integrate the optical energy from several LED lamps into a coherent illumination pattern suitable for a particular task. Optical systems utilize optical elements to redirect light emitted from the several LED lamps. Optical elements include components capable of interacting with optical energy and can include devices such as, but not limited to, filters, reflectors, refractors, lenses, etc. Light being manipulated by optical elements typically experiences some form of loss from scatter, absorption, or reflection. Thus, for example, optical energy interacting with a lens will scatter a percentage of the optical energy at each lens surface with the remainder of the optical energy passing through the lens. A typical aluminized reflector is between 92 and 95% efficient in redirecting optical energy incident upon it, with the remainder being scattered or absorbed. Optical efficiency is the ratio of total optical energy that reaches the desired target area with respect to the total optical energy produced by the light source.
In a typical prior art optical system, the optical elements are arranged symmetrically with respect to an optical axis of the light source, such as a circular parabolic aluminized reflector (PAR), a circular Fresnel lens or the like. Other prior art optical systems may exhibit elongated symmetry with respect to a longitudinal axis and/or plane bisecting the light. Elongated symmetry is commonly associated with elongated lamp formats used in some quartz halogen, fluorescent or metal halide light sources.